Prerequisites

Add-ons using the techniques described in this document are considered a legacy technology in Firefox. Don't use these techniques to develop new add-ons. Use WebExtensions instead. If you maintain an add-on which uses the techniques described here, consider migrating it to use WebExtensions.

Starting from Firefox 53, no new legacy add-ons will be accepted on addons.mozilla.org (AMO) for desktop Firefox and Firefox for Android.

Starting from Firefox 57, only extensions developed using WebExtensions APIs will be supported on Desktop Firefox and Firefox for Android.

Even before Firefox 57, changes coming up in the Firefox platform will break many legacy extensions. These changes include multiprocess Firefox (e10s), sandboxing, and multiple content processes. Legacy extensions that are affected by these changes should migrate to use WebExtensions APIs if they can. See the "Compatibility Milestones" document for more information.

Set up an easy testing environment

While you're developing your add-on, it will be very important to have a way to test and run snippets of code; development will go very slowly if you have to build and install your entire app every time you need to test something. Once all of your snippets are working together, then you can start worrying about bringing together all of the add-on files to build the complete app (bootstrap.js, etc.). You can do this using WebIDE, by connecting your device to your development workstation.

Connecting your development environment and your mobile device

You can run code snippets from your development environment on your mobile device using the WebIDE.